Semiconductor image sensors are used to sense radiation such as light. Complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) and charge-coupled device (CCD) sensors are widely used in various applications such as digital still camera or mobile phone camera applications. These devices utilize an array of pixels in a substrate, including photodiodes and transistors, that can absorb radiation projected toward the substrate and convert the sensed radiation into electrical signals.
A back side illuminated (BSI) image sensor device is one type of image sensor device. Some existing BSI image sensor fabrication processes suffer from high levels of optical cross-talk noise. Optical cross-talk noise degrades the performance of the BSI image sensor devices and is therefore undesirable. Other existing BSI image sensor fabrication processes may have somewhat acceptable optical cross-talk noise, but may result in low levels of quantum efficiency instead. A low quantum efficiency is correlated to a low signal-to-noise ratio of the BSI image sensor devices. The low-signal-to-noise ratio manifests itself as poor sensitivity for the BSI image sensor devices, which is also undesirable.
Therefore, while existing methods of fabricating BSI image sensor devices have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.